I recently found the bootstrap twitter project, which I'm going to use in my projects. Bootstrap is a toolkit from Twitter designed to kickstart development of webapps and sites. It includes base CSS and HTML for typography, forms, buttons, tables, grids, navigation, layouts, and more.
Of course, this isn't an only-Perl related topic, but I think it is a very interesting way of improvement for the user interface of any CGI::App, Catalyst, Dancer, Mojolicious, ... application.
Hope this helps in your next projects.
If you used this tool, it would be nice to hear from you...